REYKJAVIK, Iceland, April 25, 2010 /PRNewswire-FirstCall/ -- Cigarette smoking is a major cause of illness and death worldwide. But it is a complex behavior, and how much people smoke, how hard they find it to quit, and the impact of long-term smoking on health varies greatly among individuals. A substantial portion of this variability is genetic. Two years ago, deCODE discovered the first common, single-letter variation (SNP) in the sequence of the human genome, on chromosome 15q25, associated with nicotine addiction and risk of lung cancer. Today, deCODE scientists and academic colleagues from 23 institutions in a dozen countries build on this work with the discovery of common SNPs on chromosomes 8p11 and 19q13 that among smokers increase the number of cigarettes smoked per day (CPD), a measure of nicotine addiction, and increase risk of lung cancer.